Fuel ethanol production in the U.S. increased by about 440% during the period from 1996 to 2007 (from 1.1 to 6.5 billion gallons per year) and world ethanol production reached about 13.1 billion gallons per year in 2007. Fuel ethanol plants under construction/expansion are expected to double current U.S. production capacity, and legislation has been passed that could increase fuel ethanol demand by more than 600% by 2022.
Two most commonly used types of additives in fuel ethanol include denaturants and corrosion inhibitors, the use of which is growing concomitantly with the growth in fuel ethanol production. Inaccurate dosing of such additives can create a multitude of problems, including noncompliance with ASTM D-4806. For example, underdosing of corrosion inhibitor can lead to corrosion problems, whereas overdosing wastes chemicals and causes higher production costs. High dosages of some fuel ethanol corrosion inhibitors have also been linked to increases in intake valve deposits, which can cause substantial engine operational issues.
Inaccurate dosing of denaturant causes significant government regulatory and legal problems. Releasing inaccurately dosed batches of fuel ethanol would likewise violate ASTM D-4806. Both underdosing and overdosing of denaturant leads to out-of-specification results that in turn lead to higher production/shipping costs and delays due to rework of batches.
The maximum specification range currently allowed in the U.S. for denaturant is typically about 1.96 to 4.76% by volume. Due to the cost differential between ethanol and denaturant, it is valuable for a fuel ethanol plant to have the ability to be as close as possible to the upper or lower edge of denaturant dosage specification range. When ethanol costs exceed denaturant costs, for instance, it is desirable for the fuel ethanol plant to be at the high dosage edge of denaturant specification range to keep production costs to a minimum. On the other hand, when denaturant costs more than ethanol, it is desirable for the fuel ethanol plant to be at the low dosage edge of denaturant specification range.
To operate near either edge of the additive dosage specification range requires highly accurate and precise measuring/dosing of additive concentration. Presently, fuel ethanol plants tend to dose additives via splash blending and/or based on how “long” a chemical feed pump is “on” with a “constant flowrate assumed” or sometimes based on flowmeters or depth gauges. Even when such flowmeters are regularly and properly calibrated, proper dosage rates are not always achieved. Very rarely (if ever) is dosage of ethanol additives directly measured. Also, batch-to-batch variations and the complex chemical nature of ethanol additives increase difficulty of precisely and accurately measuring additive dosages with currently used methods.
There thus exists an ongoing need to develop methods of accurately and efficiently monitoring and controlling additive concentrations in fuel ethanol production plants. Such methods would allow the fuel ethanol producer to easily minimize costs of production by adjusting formulations based upon raw material costs and to maximize the quality and value of the fuel ethanol product.